Sheet diverters may range from the collating apparatus associated with an office copier, to sheet or web handling devices employed in the manufacture of paperboard articles, to sheet diverters specifically adapted to collate signatures to be used in binding or otherwise assembling books, magazines or newspapers. Each of these environments presents a somewhat different challenge in designing an efficient diverter or collator, but the same objective applies to the entire class of apparatus, namely, accurately routing selected flexible webs or ribbon sections along a desired collating path to achieve a desired order.
In the printing industry, an image is repeatedly printed on a continuous web or substrate such as paper. The ink is dried by running the web through curing ovens. In a typical printing process, the continuous web is subsequently slit (in the longitudinal direction which is the direction of web movement) to produce a plurality of continuous ribbons. The ribbons are aligned one on top of the other, folded longitudinally, and then cut laterally to produce a plurality of multi-paged, approximately page length web segments, termed signatures. A signature can also be one printed sheet of paper that has or has not been folded. It is often desirable to transport successive signatures in different directions or paths. In general, a sheet diverter operates to route a signature along a desired one of a plurality of paths.
A sheet diverter in a folder towards the end of a printing press line must be operable at the high speeds of the press line, typically in excess of 2,000-2,500 feet per minute (fpm). It is desirable to run both the press, folder and other equipment in the printing press line at the highest speed possible to produce as many printed products as possible in a given amount of time. However, the physical qualities of printed paper or similar flexible substrates moving at a high rate of speed can result in undesirable whipping, dog-earring, tearing, smearing of the ink, or bunching of the substrate. Additionally, impact between the leading edge of a signature and a diverter wedge may result in the leading edge of the signature being dented or dog-eared or damaged in other ways. Moreover, the trailing edge of a signature may slap against the top edge of a diverter wedge, resulting in tears, dog-ears or other damage to the trailing edge. Damaged signatures may be of reduced or unacceptable quality and may also lead to jams in the folder, resulting in downtime, repair expense and much wasted paper.
Another problem which occurs when operating a press and a folder at high speeds is that signatures may be routed to an undesired one of a plurality of collation paths. As the leading edge of a signature approaches the apex of a diverter wedge, depending on the stiffness of the signature and due to the relationship between the diverter and the diverter wedge, the signature may be delivered to the wrong side of the diverter wedge thereby sending the signature down the wrong collation path. This leads to jams in the folder causing delays and expense.
Yet another problem when operating a printing line at high speeds concerns ink offset in the diverter. As a signature impacts a diverter wedge, non-dried ink may transfer to the surface of the diverter wedge. As successive signatures contact the diverter wedge, the ink transferred to the diverter wedge may undesirably pass to the other signatures. The greater the impact of the signatures against the diverter wedge, the greater the likelihood of ink offset.
Many of the foregoing defects become more prevalent above certain speeds of the printing press and folder. For example, such defects may occur when the press is run at speeds greater than 2,500 fpm, but may not occur when the press is run at a slower speed, for example, 2,200 fpm. As printing press speed capabilities have increased, it has become increasingly important to provide a system which allows for individual signatures to be directed down any one of a plurality of selected collation paths without damaging the leading or trailing edge of each signature or causing jams.
U.S. Pat. No. 4,373,713 discloses a diverter mechanism placed in a path of a stream of cut sheets comprising a pair of rotary diverters with raised cam surfaces used to divert and guide the sheets. A tapered guide has a pair of diverging guide surfaces and has its upstream tapered end interposed between the rotary diverters with raised cam surfaces and diverging tapes.
A sheet diverter for signature collation and a method thereof is described in U.S. Pat. No. 4,729,282, assigned to Quad/Tech, Inc., of Pewaukee, Wis., and is hereby incorporated by reference. The '282 patent discloses a sheet diverter including an oscillating diverter guide member that directs successive signatures to opposite sides of a diverter wedge. As set forth in the '282 patent, the diverter design disclosed in the '713 patent is not viewed as workable in light of the high speeds sought to be attained nor is it seen to be particularly reliable in reducing jamming tendencies which are expected to arise in these settings.